Proton Therapy for 166 Patients with Iris Melanoma: Side Effects and Oncologic Outcomes.

To investigate the oncologic and functional outcomes of a large cohort of patients with a favorable stage of circumscribed and diffuse iris melanoma who underwent primary proton treatment and the risk factors related to initial tumor characteristics and the treatment field architecture. Retrospective, single-center, case study. We reviewed 225 patients with iris melanoma who were consecutively treated with proton beam therapy at our institution between 1998 and 2020. We performed Kaplan-Meier time-to-event analyses and multivariate Cox proportional hazard analyses to identify the impacts of tumor characteristics and target volumes on oncologic and functional outcomes. We measured local tumor control, eye preservation rates, metastasis-free survival, cataract and glaucoma-directed surgery, intraocular pressure, and changes in visual acuity. Of the 192 patients with tumors confined to the iris (T1a-c) who underwent proton therapy as primary treatment, a total of 166 patients (mean age, 58.4 years; 88 women) with a minimum follow-up of 6 months were included. Multifocal or diffuse tumor spread was present in 77 (46.4%) patients. The median follow-up time was 54.0 (interquartile range, 27.4-91.8 months) months. Local recurrence occurred in 2 patients (1.2%) with circumscribed iris melanoma. Enucleation was a rare event (n = 5, 3%) and no patient developed metastatic disease. A large-treatment field (full aperture, involving > 10 clock hours) was identified as a risk factor for the development of secondary glaucoma (hazard ratio [HR], 6.3; P < 0.001) and subsequent surgical interventions (HR, 10.85; P < 0.001). The large-treatment field group showed a significant decline in visual acuity (logarithm of the minimum angle of resolution > 0.3; log-rank P < 0.0001), which was associated with secondary glaucoma (HR, 3.40; P = 0.002). Proton therapy provides an effective, noninvasive treatment option for patients with a favorable stage of iris melanoma. Irradiation of the anterior segment for up to 10 clock hours is associated with a low risk of the development of secondary glaucoma and vision loss. Proprietary or commercial disclosure may be found after the references.

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